AMGStep: use `override` keyword; use `= default` for default constructor

dune/solvers/iterationsteps/amgstep.hh

@@ -34,7 +34,7 @@ class AMGStep
 public:
 
     /** \brief Default constructor */
-    AMGStep () {}
+    AMGStep () = default;
 
     /** \brief Constructor which initializes and sets up an algebraic hierarchy
         \param smootherArgs  Arguments for the smoother.  See the dune-istl documentation for details
@@ -69,10 +69,10 @@ public:
 
     /** \brief Sets up an algebraic hierarchy
      */
-    virtual void preprocess();
+    void preprocess() override;
 
     /** \brief Perform one iteration */
-    virtual void iterate();
+    void iterate() override;
 
     /** \brief Arguments for the smoother.  See the dune-istl documentation for details */
     SmootherArgs smootherArgs_;